*{
    margin: 0;
    padding: 0;
}
html, body{
    height: 100%;
    overflow: hidden;
}
.wrap{
    height: 100%;
    overflow: auto;
    .content{
        height: 200%;
        .returntop{
            position: absolute;
            right: 50px;
            bottom: 50px;
            width: 50px;
            height: 50px;
            background-color: #acf;
        }
    }

}